A longitudinal study involving 455 Black young adults living in Canada investigated whether gender and autonomous motivation influenced the relationship between perceived racism threat and Black Lives Matter (BLM) activism, and whether BLM activism influenced life satisfaction over time. A moderated mediation analysis using PROCESS Macro Model 58 tested the indirect effect of autonomous motivation on the relationship between perceived racism threat and BLM activism varying by gender. Multiple linear regression assessed how well BLM activism predicted life satisfaction. Black women perceived greater racism threat than Black men related to increases in BLM activism via the influence of autonomous motivation. BLM activism had a positive influence on life satisfaction over time, regardless of gender. This research suggests Black young women are playing pivotal roles in the BLM movement and helps us understand how motivation may be influencing involvement and well‐being in social justice issues.